1. Field of the Invention
The present invention relates to radio communication terminals and receiving methods, and particularly to a radio communication terminal with automatic gain control (AGC) and to an antenna switching method.
2. Description of the Related Art
In a Wideband Code Division Multiple Access (W-CDMA) system of the related art, a radio communication terminal has a plurality of antennas for RX(Receiving) diversity communications. In the radio communication terminal, in order to improve receiving signal quality, the radio signals received through the antennas are combined with one another so that an optimal gain can be obtained. The radio communication terminal is small. Accordingly, it is difficult to provide a complicated circuit for executing the above operation in the radio communication terminal. Radio communication environments of the terminal are not constant since the radio communication terminal always moves with its user. Therefore, the radio communication terminal needs more complicated receiving processes.
In addition, a receiving method that provides simple antenna switching procedure. Switching of the antennas is made based on the received signal power. An AGC receiver in the radio communication terminal measures the received power intensity. The AGC receiver amplifies a received radio signal by feedback-controlling. For example, Japanese Unexamined Patent Application Publication No. 2002-135346 discloses an AGC circuit that calculates the power of an input signal during a short period. This AGC circuit makes it possible to obtain a targeted reception level at high speed in the beginning of operation. However, an AGC technology of the related art has a possibility that an unstable received radio signal caused by antenna switching may be used as received data.